Prosthetic foot

ABSTRACT

A prosthetic foot is provided with a forefoot spring, a heel spring and a base spring. The base spring is connected to the heel spring and to the forefoot spring. The base spring has receiving means for the forefoot spring and the heel spring, into which receiving means the heel spring and the forefoot spring can be inserted. The heel spring is connected to the forefoot spring via a coupling element, and the coupling element extends forwards along the forefoot spring at least via one portion thereof.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a prosthetic foot with a forefoot spring, aheel spring and a base spring, the latter being connected to the heelspring and to the forefoot spring.

Background Description

U.S. Pat. No. 6,719,807 B2 describes a prosthetic foot with atwo-dimensional resilient forefoot part, a two-dimensional resilientheel part, and a substantially rigid carrier part. One end of each ofthe forefoot part and heel part is connected to the carrier part, andthe forefoot part and the heel part each work independently of therespective other part. The forefoot part extends forwards andsubstantially unidirectionally from its connection to the carrier part,while the heel part extends rearwards and substantially unidirectionallyfrom its connection to the carrier part.

U.S. Pat. No. 5,181,933 describes a prosthetic foot with a securingmeans for facilitating the operation of engaging the foot with the stumpof a prosthetic foot user. A large number of curved, energy-storing footareas are secured on the securing means and extend downwards in order torest on the ground. Each of the curved portions has an ankle area, thefoot areas interact independently of each other with the ground, and thecurved portions having a similar shape. A heel spring is secured in areleasable manner on a forefoot portion and extends rearwards. A similarconstruction is described in U.S. Pat. No. 5,514,185.

U.S. Pat. No. 5,776,025 describes a prosthetic foot with a securing areaon which a downwardly extending, curved and partially slit spring issecured. A continuous spring with a heel area and a forefoot area issecured on the front lower end area of the spring.

The continuous spring has a curved shape. A similar construction isdescribed in U.S. Pat. No. 6,071,313.

US 2005/0203640 A1 describes a prosthetic foot with a resilient anklearea. Starting from an attachment adapter, an upper securing portion ofthe forefoot area extends obliquely rearwards and downwards and, after acurve, merges into a forwardly and downwardly extending arch portion,which ends in a toe portion. A heel spring extends in parallel as far asthe ankle area, and, after the curve, a first portion assumes a greaterinclination than the arch portion. The first portion is followed byanother curve, such that a heel portion extends obliquely downwards andrearwards. The heel spring is therefore S-shaped. A lower base spring isconnected to the rear end of the heel spring and to the toe area, and acushion can be arranged between the toe portion and the front part ofthe base spring.

GB 306,313 describes a prosthetic foot with a U-shaped frame forattachment to a below-knee shaft, on which a heel part is arranged whichis likewise U-shaped and is arranged at a right angle to the frame. Afront part corresponding substantially to the contour of a natural footis arranged on the heel part. The front part is mounted elastically viaresilient rods.

U.S. Pat. No. 4,721,510 describes a prosthetic foot having a hollowelastomer cosmetic shell with a relatively large internal space. In thearea of the insertion opening, the sole has a thickened area to which ananchor plate is secured. A reinforcement plate is arranged on the anchorplate, and a stiffening spring with a forefoot spring area and a heelspring area is secured on the reinforcement plate. Arranged above thespring is a wedge on which the springs bear in the event of overloading.

U.S. Pat. No. 4,822,363 describes a prosthetic foot with an elongate andcurved spring which has a proximal securing branch and, adjoining thelatter, a forwardly extending forefoot branch. Arranged on the securingbranch, there is a heel spring, which is of a curved design, eitherapproximately S-shaped or L-shaped. In an alternative embodiment, a heelspring is secured releasably in the forefoot area and extends rearwardswith a slight curvature.

U.S. Pat. No. 2,475,372 describes a prosthetic foot with an upper areaon which a below-knee shaft can be secured in an articulated manner. Ametatarsal area is mounted in an articulated manner on a heel area. Themetatarsal area is adjoined by a forefoot area that is articulatedthereon. The forefoot area is mounted resiliently via a springmechanism.

U.S. Pat. No. 5,258,039 describes a resilient prosthetic foot with aforefoot spring and a heel portion that are connected to each other byan elastomeric ankle element. The forefoot spring has a longitudinalslit. The heel spring has a C-shaped design. In an alternativeembodiment, the prosthetic foot is designed in one piece.

U.S. Pat. No. 6,669,737 B2 describes a resilient foot insert for anartificial foot, comprising at least two springs which in a side view,in an unloaded state, enclose between them an approximately triangularspace and form a roof area. A securing element is arranged in the roofarea. Starting from the securing element, a heel portion extendsrearwards and downwards in a concave curve, while a forefoot portionextends forwards and downwards in a similarly concave curve. A separatebase spring is connected, in the heel area and in the toe area, to theheel portion and to the forefoot portion.

U.S. Pat. No. 6,099,572 describes a resiliently elastic foot insert withat least one leaf spring, which comprises at least two leaf springelements which are coupled in parallel and are arranged next to eachother. The leaf spring elements are connected to each other at both endsand, between the two end areas, have a clearance from each other. Theconnection is designed to be rigid in terms of torque in at least one ofthe two end areas.

SUMMARY OF THE INVENTION

The Otto Bock company has produced a resilient foot insert called theIC30 Trias, in which a dual heel spring and a dual forefoot spring aresecured on a proximal adapter. A base spring is secured on the rear endof the dual C-shaped heel spring. The base spring is likewise fixed tothe front end of the forefoot spring.

It is an object of the present invention to make available a prostheticfoot that provides a comfortable rollover. Another object of theinvention is to make available a prosthetic foot that can also be usedon patients with a high activity level. Finally, a further object of theinvention is to make available a prosthetic foot that is easy to produceand that can be easily adapted to different users.

According to the invention, these objects are achieved by a prostheticfoot having the features of the main claim. Advantageous embodiments anddevelopments of the invention are set forth in the dependent claims.

In the prosthetic foot according to the invention, with a forefootspring, a heel spring and a base spring, the latter being connected tothe heel spring and to the forefoot spring, provision is made that thebase spring has receiving means for the forefoot spring and the heelspring, into which receiving means the heel spring and the forefootspring can be inserted. The receiving means permit a modularconstruction of the prosthetic foot and allow different base springs tobe used that are adapted to the weight, the mobility grade and otheraspects of the prosthesis user. They can be adapted very easily byinserting the forefoot spring and the heel spring into the respectivereceiving means. The receiving means can held the forefoot spring andthe heel spring with a form fit, such that there is no need for adhesivebonding or other forms of attachment in order to create a connection,and thus a force coupling, between the forefoot spring and the heelspring.

The receiving means can be designed as pockets into which the heelspring and the forefoot spring are inserted. In principle, no furtherlocking is needed if the forefoot spring and the heel spring aretensioned in the assembled state and subject the receiving means to aforce that forces the receiving means outwards, that is to say the rearreceiving means rearwards and the front receiving means forwards.

The pockets can be of a closed design and have an insertion opening intowhich the forefoot spring and the heel spring are inserted. The closeddesign of the pockets provide protection for the sensitive end area ofthe springs, such that destruction, for example in the case offibre-reinforced composite springs, is not to be expected. The insertionopenings preferably lie opposite each other, such that the directions ofinsertion are counter to each other, which has the effect that the basespring is subjected to tension after insertion of the heel spring andthe forefoot spring.

Pretensioning means optionally can be arranged in the receiving meansthat pretensions the heel spring and/or the forefoot spring against thebase spring or the receiving means, in order to provide additionalsecuring of the base spring on the forefoot spring and on the heelspring. The pretensioning means can be designed to include a spring orelastomer element and can provide pretensioning or an additionalpretensioning of the forefoot spring and of the heel spring against thereceiving means or the base spring. The pretensioning means can alsoform a clip connection to also permit a form-fit locking, such that thepretensioning elements can also serve as fixing means. Thus, lockingmeans are also provided in the receiving means in order to lock the basespring to the forefoot spring and/or to the heel spring, in particularwith a form-fit locking action. Corresponding locking means can beprovided on the forefoot spring and the heel spring and engage with thelocking means in or on the receiving means. Pretensioning elements canbe cast into the receiving means, pushed in, bonded in or secured on theheel spring and/or the pretensioning means.

The base spring can be designed as a tension member, for example as astrap, which is flexible but not elastic against bending forces ormoments and preferably not elastic in the longitudinal direction of thebase spring.

The base spring can be designed as a spring, arching upwards in theunloaded state of the prosthetic foot, so as to permit inward deflectionin the event of loading of the heel, loading of the forefoot or highaxial loading, by means of the arch being reduced and the base springlengthening. The stiffness of the base spring, and therefore therollover of the prosthetic foot, can be influenced by the degree ofarching.

The base spring can be pretensioned with a tensile stress in theunloaded state of the prosthetic foot, such that the ends of the basespring are forced in different directions. In the case of an arched basespring, an applied tensile stress also causes a bending moment withinthe spring.

The base spring can be designed as an injection-moulded part, especiallywhen designed as a spring, in order to achieve rapid and inexpensiveproduction. The base spring can also be designed in several parts andput together in a joining method, for example by severalinjection-moulded parts being connected to one another. It is alsopossible for the base spring to be made of different materials that areconnected to one another by injection moulding. For example, springelements or rigid components can be placed into the mould andencapsulated. It is also possible for individual components of the basespring to be placed into the injection-moulding tool and for othercomponents to be injected thereon. The individual parts of the basespring can likewise be produced by multi-component injection moulding,for example by two-component injection moulding. The base spring can beproduced from a composite material or can have parts that are made of acomposite material. Examples of composite materials that can be used arefibre-reinforced plastics, for example plastics reinforced with carbonfibre or reinforced with glass fibre.

The base spring can have a curved middle portion, which is adjoined atboth ends by the receiving means. The receiving means can be screwed on,clipped on or injected on. The receiving means can also be integrallyformed on the middle portion. The middle portion can be designed, forexample, as a beam spring made of a fibre-reinforced plastic, onto whichreceiving means are injected.

The heel spring can be connected to the forefoot spring via a couplingelement, such that there is no direct join of the heel spring to theforefoot spring. The coupling element serves to make available a furtheradjustment element, since the design of the coupling element, both interms of its elasticity and also its geometric nature, can be used tomodify the resiliency characteristics of the prosthetic foot.

The forefoot spring and the coupling element can be arranged extendingparallel to each other at least in part, such that they supplement eachother in terms of their elasticity. The coupling element thus extendsforwards along at least a part of the forefoot spring, and parallel tothe forefoot spring, at least in the unloaded state. The couplingelement can have an upwardly directed portion and a forwardly directedportion, such that a substantially L-shaped structural part is presentwhich extends in a manner corresponding to the forefoot spring. Theangle of opening of the L-shaped coupling element can be different thanthe angle of opening of the forefoot spring. The upwardly directedportion is likewise oriented substantially vertically, such that only aslight spring action is made available from the vertically orientedportion when a perpendicular downwardly acting load is placed on theprosthetic foot. The upwardly directed portion can have an S-shapedconfiguration, as a result of which its spring action can bestrengthened.

The heel spring can be secured on a front area of the coupling element,so as to make available a sufficient length of the heel spring. Thelonger a spring is, the more sensitively it is able to react to loadsoccurring at its ends. Moreover, coupling the front area of the heelspring to the front area of the coupling element affords the possibilityof also using the elasticity of the forwardly directed portion of thecoupling element in order to obtain a comfortable heel strike.

The coupling element can extend forwards along at least part of theforefoot spring, and parallel to the forefoot spring, such that thecoupling element provides an additional spring action via the forwardlydirected portion. For this purpose, the coupling element is designed asa spring, for example made of a fibre-reinforced plastic.

The heel spring can be curved and, from its rear end, extends forwardsand upwards and has a curvature such that the front end area is orientedsubstantially horizontally or at a slight downward incline. A precisesetting of the spring characteristics can be achieved by means of theundulating design of the heel spring.

The forefoot spring can have a substantially straight forefoot portionwhich is oriented at a downward inclination towards the front and which,starting from the curve that follows the substantially verticallyoriented portion, can extend forwards rectilinearly. In the toe area, itcan have a flattening, which can also merge upwards into a slightcurvature in order to facilitate rollover.

A connecting means can be provided for securing the prosthetic foot to abelow-knee shaft and is arranged on the proximal end of the prostheticfoot. The connecting means can be secured, preferably by screwing, onthe proximal end of the forefoot spring and, if appropriate, on theproximal end of the coupling element. The connecting means can beprovided with a shock absorber which, in addition to axial forces, isalso able to take up torques and absorb rotation movements.

The forefoot spring can be designed as a straight flat spring, with theconnecting means arranged at a rear portion of the forefoot spring. Thecoupling element can be designed as a straight flat spring, too,arranged parallel to the forefoot spring. No vertical part of thecoupling element or the forefoot spring is needed.

The forefoot spring and the base spring can have a slit that extendsfrom the front end of the prosthetic foot, in order to permit amedial-lateral mobility of the forefoot spring and of the base spring.It is in this way possible, for example upon rollover on an inclinedplane, that not just one edge establishes the contact with the ground orwith the shoe.

The prosthetic foot can have a progressive ankle moment profile. Aprogressive ankle moment profile can be achieved through a combinationof the heel spring with a resilience element. In particular, the shapeof the resilience element can generate the progressiveness, byincreasing the cross-sectional surface that is to be compressed. Aprogressive ankle moment profile can also be generated by placing theconnecting area of the heel spring and of the coupling element on thebase spring, but only with correspondingly high loading.

At heel strike, the force can be transferred at least partially to theforefoot spring via the base spring, this being achieved by thepretensioning and coupling of the forefoot spring to the heel spring viathe base spring. The base spring thus serves as tension element, suchthat the force upon heel strike is transferred via the base spring tothe forefoot spring. Energy is partially stored in the base springespecially in the embodiment as a base spring, particularly if thelatter has an S-shaped curvature, and is then returned, since theconnections and couplings of the springs to one another has the effectthat none of them is able to act independently of the other springs.

The forefoot spring and the base spring, especially in the embodiment asa base spring, are designed, in terms of their shape and flexuralelasticity, in such a way that during rollover, when the force isinitially introduced into the ball region at the start of loading of theforefoot, the forefoot spring and the base spring come closer to eachother by means of each of them bending under increasing loading. In thisway, the springs can come to lie on each other, with the result that,starting from a defined loading level, the spring resistance can beincreased by the springs lying on each other and by the friction of thesprings on each other.

In the prosthetic foot according to the invention, with a forefootspring, a heel spring and a base spring, the latter being connected tothe heel spring and to the forefoot spring, provision is made that theheel spring is connected to the forefoot spring via a coupling element,such that there is no direct join of the heel spring to the forefootspring. The coupling element serves to make available a furtheradjustment element, since the design of the coupling element, both interms of its elasticity and also its geometric nature, can be used tomodify the resiliency characteristics of the prosthetic foot. Thecoupling element extends forwards along the forefoot spring at least viaone portion and makes available an optionally resilient portion on whichthe heel spring can be supported. The articulation of the heel spring onthe coupling element decouples the heel spring from the forefoot spring,such that a more variable adjustment of the prosthetic foot can becarried out, since the points of articulation can be chosen more freely.The connection of heel spring and forefoot spring no longer has to bemade at sites of high mechanical loading, and instead can be made atlocations that can be chosen relatively freely.

The forefoot spring and the coupling element can be arranged extendingparallel to each other at least in part, such that they supplement eachother in terms of their elasticity. The coupling clement thus extendsforwards along at least a part of the forefoot spring, and parallel tothe forefoot spring, at least in the unloaded state. The couplingelement can have an upwardly directed portion and a forwardly directedportion, such that a substantially L-shaped structural part is presentwhich extends in a manner corresponding to the forefoot spring. Theangle of opening of the L-shaped coupling element can be different thanthe angle of opening of the forefoot spring. The upwardly directedportion is likewise oriented substantially vertically, such that only aslight spring action is made available from the vertically orientedportion when a perpendicular downwardly acting load is placed on theprosthetic foot. The upwardly directed portion can have an S-shapedconfiguration, as a result of which its spring action can bestrengthened.

The heel spring can be secured on a front area of the coupling element,so as to make available a sufficient length of the heel spring. Thelonger a spring is, the more sensitively it is able to react to loadsoccurring at its ends. Moreover, coupling the front area of the heelspring to the front area of the coupling element affords the possibilityof also using the elasticity of the forwardly directed portion of thecoupling element in order to obtain a comfortable heel strike.

The coupling element can extend forwards along at least part of theforefoot spring, and parallel to the forefoot spring, such that thecoupling element provides an additional spring action via the forwardlydirected portion. For this purpose, the coupling element is designed asa spring, for example made of a fibre-reinforced plastic.

The heel spring can be curved and, from its rear end, extends forwardsand upwards and has a curvature such that the front end area is orientedsubstantially horizontally or at a slight downward incline. A precisesetting of the spring characteristics can be achieved by means of theundulating design of the heel spring.

The forefoot spring can have a substantially straight forefoot portionwhich is oriented at a downward inclination towards the front and which,starting from the curve that follows the substantially verticallyoriented portion, can extend forwards rectilinearly. In the toe area, itcan have a flattening, which can also merge upwards into a slightcurvature in order to facilitate rollover.

The base spring can have receiving means for the forefoot spring and theheel spring, into which receiving means the heel spring and the forefootspring can be inserted such that, in the assembled stale, the forefootspring and the heel spring are inserted and held in the receiving means.The receiving means permit a modular construction of the prosthetic footand allow different base springs to be used that are adapted to theweight, the mobility grade and other aspects of the prosthesis user.They can be adapted very easily by inserting the forefoot spring and theheel spring into the respective receiving means. The receiving means canhold the forefoot spring and the heel spring with a form fit, such thatthere is no need for complicated adhesive bonding or other forms ofattachment in order to create a connection, and thus a force coupling,between the forefoot spring and the heel spring.

The receiving means can be designed as pockets into which the heelspring and the forefoot spring are inserted. In principle, no furtherlocking is needed if the forefoot spring and the heel spring aretensioned in the assembled state and subject the receiving means to aforce that forces the receiving means outwards, that is to say the rearreceiving means rearwards and the front receiving means forwards.

The pockets can be of a closed design and have an insertion opening intowhich the forefoot spring and the heel spring are inserted. The closeddesign of the pockets provides protection for the in some casessensitive end area of the springs, such that destruction, for example ofthe fibre structure in the case of fibre-reinforced composite springs,is not to be expected. The insertion openings preferably lie oppositeeach other, such that the directions of insertion are counter to eachother, which has the effect that the base spring is subjected to tensionafter insertion of the heel spring and of the forefoot spring.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the invention are explained in more detailbelow with reference to the attached figures.

FIG. 1 shows a prosthetic foot in an exploded and perspective view;

FIG. 2a shows a side view of a prosthetic foot according to FIG. 1;

FIG. 2b shows a plan view of the prosthetic foot according to FIG. 1;

FIG. 3 shows an exploded side view of the prosthetic foot according toFIG. 2 a;

FIGS. 3 a, 3 b show variants of the FIG. 3 embodiment;

FIGS. 4 a, 4 b show a base spring in two perspective views;

FIG. 5a shows a side view of an alternative embodiment of the prostheticfoot;

FIG. 5b shows an exploded and perspective view of the prosthetic footaccording to FIG. 5 a;

FIG. 6a shows a side view of a further alternative embodiment of theprosthetic foot with a shock absorber,

FIG. 6b shows an exploded view of the foot according to FIG. 6 a;

FIG. 7 shows an exploded and perspective view of a further embodiment ofthe invention;

FIG. 7a shows an exploded side view of the embodiment of FIG. 7;

FIG. 7b shows a side view of the assembled embodiment of FIG. 7;

FIG. 8 illustrates a modified base spring having cylindrical orfrusto-conical receiving means for receiving ends of the forefootspring; and

FIG. 9 illustrates a further variation of the caps shown in the FIG. 7embodiment.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

In FIG. 1, a prosthetic foot 1 comprising a forefoot spring 2, a heelspring 3 and a base spring 4 in form of a base spring is shown in anexploded and perspective view. The forefoot spring 2 has a substantiallystraight vertical portion 22 which, after a curvature, merges into asubstantially straight forefoot portion 21. The forefoot portion 21extends forwards at a downward incline and can have a further bend inthe toe area, such that the toe area is oriented substantiallyhorizontally or is curved slightly upwards. In the front end area of theforefoot portion 21, sleeves or caps 24 can he arranged which at leastpartially enclose the forefoot spring 2. The forefoot spring 2 can bemade of a plastic or of a composite material, in particular afibre-reinforced plastic. A connecting means 6 in the form of aconventional adapter is positioned on the vertical portion 22. It issecured by bolts 9, which are guided through a securing plate orreinforcement plate 8. The bolts 9 pass through the reinforcement plate8, a coupling element 5 and the vertical portion 22 of the forefootspring 2 and are screwed into the adapter 6.

By means of the bolts 9, the forefoot spring 2 is coupled mechanicallyto the coupling element 5 in the proximal area of the vertical portion22. The coupling element 5 likewise has a vertical portion 51, which isadjoined by a forwardly directed portion 52. The transition between thevertical portion 51 and the front portion 52 is likewise effected via abend, which is arranged in the area of the natural ankle. The couplingelement is likewise designed as a spring and extends with the frontportion 52 substantially parallel to the forefoot portion 21 of theforefoot spring 2.

A front area 521 of the coupling element 5 is provided with boresthrough which screws 10 are guided. In the front area 521 of thecoupling element 5, the screws 10 provide a mechanical connection to thefront end area 31 of the heel spring. The front end area 31 of the heelspring 3 is likewise provided with bores or recesses through which thescrews 10 extend, and the screws 10 are fixed in sleeves 11.

The heel spring 3 is designed with a slight curve and slopes gentlydownwards in the front end area, whereas the curvature extends in theopposite direction at the rear end 32 of the heel spring, such thatthere is a substantially horizontal orientation in the rear end 32. Aspring element 7 in the form of an elastomer component is arrangedbetween the heel spring 3 and the ankle area of the coupling element 5.

The rear end 32 of the heel spring 3 can likewise be lined with a sleeveor cap 34, which can be inserted into a rear receiving means 43 of thebase spring 4.

The receiving means 43 of the one-piece base spring 4 is designed as apocket, which forms a closed cap. The base spring 4 is arched slightlyupwards and also has, at the front end, receiving means 42 for receivingthe forefoot spring 2. The design of the forefoot spring 2 and also ofthe base spring 4 is explained in more detail below.

FIG. 2a shows the prosthetic foot 1 in the assembled state. It will benoted that the bolts 9 extend through both the coupling element 5 andalso the forefoot spring 2 and engage in threads in the adapter element6. The vertical portions 22, 51 of the forefoot spring 2 and of thecoupling element 5 extend parallel to each other and substantiallyvertically, both vertical portions 22, 51 being adjoined by a bent anklearea that has a curvature, for example a smooth curvature in the shapeof a sector of a circle. The forwardly directed portion 52 of thecoupling element 5 extends along part of the length of the forefootportion 21, parallel to the forefoot portion 21, and can either bear onthe underside of the forefoot portion 21 or have a small gap betweenitself and the forefoot portion 21. A wedge 12 in the ankle area of thecoupling element 5 has a straight underside, such that, after the startof the curvature in the ankle area, there is a rectilinear continuationfor supporting the spring element 7.

It will also be seen from FIG. 2a that the screws 10 end flush on theupper face of the front area 521 of the coupling element 5 and extendthrough both the coupling element 5 and also the heel spring 3. The heelspring 3 has an upwardly curved profile and extends rearward beyond thevertical portion 22, 51 of the forefoot spring 2 and of the couplingelement 5. The rear end 32 is received in the receiving means 43 of thebase spring 4. The base spring 4 has a slight upward curvature so as tohe able to lengthen at heel strike, in order to provide an additionalspring action. The front end of the base spring 4 is likewise providedwith a receiving means 42, into which the front end of the forefoot area21 of the forefoot spring 2 engages with a form fit.

In the assembled state shown, the front end of the forefoot spring 2 andthe rear end 32 of the heel spring 3 press in different directionsagainst the receiving means 42, 43 designed as pockets, such that theforefoot spring 2 and the heel spring 3 are tensioned against eachother. This has the effect that the base spring 4 is under tensilestress, such that the upwardly directed arch tends to be pressed down.The tension between the heel spring 3 and the forefoot spring 2 isapplied and maintained via the resilient coupling element 5. It will beseen from the plan view in FIG. 2b that both the base spring 4 and alsothe forefoot spring 2 have a slit 46, 26 that extends alongapproximately the first third of the forefoot spring 2. By means of theslits 26, 46, it is possible to permit and to compensate for differentloading in the medial-lateral direction in the forefoot area.

FIG. 3 shows an exploded and perspective side view of the prostheticfoot 1. The figure clearly shows the forefoot spring 2 with the verticalportion 22, the curved ankle portion 23 in the shape of a sector of acircle, the forefoot area 21 and the sleeves 24 for insertion into thefront receiving means of the base spring 4. The adapter 6 with thepyramid connector for connection to the other components of a prosthesisis mechanically secured, together with the coupling element 5, on thevertical portion 22 of the forefoot spring 2 by means of the bolts 9 andthe reinforcement plate 8. The coupling element 5, which can also bedesignated as a securing spring, also has a vertical portion 51, aforwardly inclined front portion 52 and an ankle portion 53, which isdesigned corresponding to the ankle portion 23 of the forefoot spring 2.Arranged on the outer side of the curve is the wedge 12, which isprovided as a continuation and bearing for an additional spring element7. Instead of a spring element 7, it is also possible to provide awedge-shaped spring element 7′, as shown in FIGS. 3a and 3 b, thatprevents or restricts relative movement between the ankle area 53 andthe wedge 12 to the rear end of the heel spring 3.

FIGS. 3a and 3b show a variant of the embodiment according to FIG. 3 inan assembled state. In FIGS. 3a and 3 b, the spring element 7 has beenreplaced with a wedge-shaped spring element 7′. In FIG. 3a the springelement 7′ is not inserted. The prosthetic foot can be used without thespring element 7′, if the patient prefers a “soft” heel. For fixing thespring element 7′ a retainer element 57 in form of a protrusion isprovided at the coupling element 5. The wedge-shaped spring element 7′is inserted or slid in the tapered gap between the coupling element 5and the heel spring 3 and is held there form-fittingly by the retainerelement 57. The assembled state is shown in the FIG. 3 b. With such aninstalled spring element 7 it is possible to vary the stiffness of theheel. With an installed spring element 7′ a stiffer heel is providedthan without the spring element 7′. Various different stiffnesses of thespring element 7′ can be provided to adopt the stiffness of theprosthetic foot to the preferences of the patient during the tread.

FIGS. 4a and 4b show different views of a base spring 4. The base spring4 has front and rear receiving means 42, 43 with insertion openings 421,431, such that the respective portions 24, 34 of the forefoot spring 2and of the heel springs can be inserted and held with a form fit in thereceiving means 42, 43. The slit 46, which is formed almost to thehalfway point of the base spring 4, permits a medially/laterallydirected compensating movement. In the middle portion 44 of the basespring, an arch is provided which is directed upwards in order to makeavailable an additional spring action. Locking elements, tensioningelements or form-fit elements can be arranged in the receiving means 42,43 so as to be able to hold the springs 2, 3 securely in the receivingmeans 42, 43. These locking elements can be designed as projections, forexample, and the pretensioning means can likewise be designed as springsor elastomer elements that are arranged in and/or on the receiving means42, 43. Because of the arrangement of the slit 46 in the base spring 4,two receiving means 42 are provided in the forefoot area of the basespring 4. In a design of the forefoot spring without a slit, only onereceiving means 42 is provided and needed. The base spring 4 can be madefrom an injection moulded part and be designed in one piece. It is alsopossible for a reinforcing element, for example a curved andfibre-reinforced plastic spring, to he placed in an injection mould andthen encapsulated with a plastic, such that the receiving means 42, 43are formed integrally on the base spring. It is also possible inprinciple for the base spring 4 to be designed in several pieces, suchthat the receiving means 42, 43 are secured on the middle portion 44,for example by screwing, adhesive bonding, welding or some other way.

FIGS. 5a and 5b show an alternative embodiment of the invention. Thebasic structure of the prosthetic foot 1 corresponds to that shown inFIGS. 1 to 4. Identical reference signs designate identical structuralparts. In contrast to the design according to FIGS. 1 to 4, theprosthetic foot 1 according to FIGS. 5a and 5b does not have a verticalportion 22, 51 on the forefoot spring 2 and the coupling element 5. Theforefoot spring 2 and the coupling element 5 are thus designed assubstantially straight springs, and the adapter 6 is once again securedby screws that pass through the coupling element 5 and the forefootspring 2. Such a prosthetic foot is of advantage when there is aconsiderable below-knee length and when, as a result, the upperattachment point of the prosthetic foot 1 cannot be moved upwards to thedesired extent. In addition, the adapter 6, at the surface facing theforefoot spring 2, is rounded or has a haunch so that there is no edgeor rim facing to the upper surface of the forefoot spring. If a rim oredge is acting on the upper surface of the forefoot spring 2 and theadapter 6 is moved relatively to the forefoot spring, very high stressis applied to the forefoot spring, which is usually made of fibercomposite material. By pressing a rim or edge onto the surface of thespring, a very small indentation is made, which may lead to a weakeningof the material and to wear of the forefoot spring. With a rounded andsmooth surface of the adapter 6, a kind of wedge is created in which anelastomer can be integrated.

FIGS. 6a and 6b show an alternative embodiment of the invention. Thebasic structure of the prosthetic foot 1 corresponds to that in FIGS. 1to 4. In addition to the customary adapter 6, a shock absorber 61 isalso provided that is able to take up axial loads and torques about thevertical axis. The shock absorber 61 serves to further increase thecomfort level and affords further possibilities of adjustment, to ensurethat the rollover can be adapted to the wishes of the prosthetic footuser. The stiffness can be adjusted by exchanging the absorption elementfor one with greater stiffness or by increasing the pretensioning in theabsorption element of the shock absorber 61. The shock absorber 61 canalso comprise a vacuum pump.

The base spring 4 is easy to produce and can be easily exchanged. It isthus possible to adapt the prosthetic foot 1 to the requirements of theparticular user. It is set up in a simple way, by inserting the frontends of the forefoot spring 2 with the caps 24 into the front receivingmeans 42 and by inserting the rear end of the heel spring 3, ifappropriate with a cap, into the rear receiving means 43, such that thebase spring 4 is held securely on the prosthetic foot 1 as a result ofthe tension between the front and rear ends of the forefoot spring 2 andheel spring 3. At heel strike, the force is transferred at leastpartially to the forefoot spring 2, by means of the arch, in the middlearea 44, stretching until the base spring 4 transfers tensile forceswithout deformation directly to the receiving means 42, which then inturn transfers forces to the forefoot spring 2. It is thus possible forall of the spring elements, namely the forefoot spring 2, the couplingelement 5, the heel spring 3 and the base spring 4, to be utilized atheel strike in order to store and then deliver kinetic energy. This hasthe effect that all of the individual spring elements 2, 3, 4, 5 arecoupled to one another and contributes to storing energy, such that eachindividual spring element 2, 3, 4, 5 can be made smaller than would bethe case if it had to perform only partial functions in isolation.

The prosthetic foot 1 according to the invention has five maincomponents, namely the forefoot spring 2, the coupling element 5, whichis secured on the forefoot spring 2, the heel spring 3, which is securedon the coupling element 5, the base spring 4, which connects the frontend 21 of the forefoot spring 2 to the rear end 32 of the heel spring 3,and the fifth component, the adapter element 6, which is designed as aconventional pyramid adapter with elements for securing to othercomponents of a prosthetic leg. The springs 2, 3, 4, 5 are preferablymade from fibre-reinforced plastic materials, in particularcarbon-fibre-reinforced plastics, which are configured as so-calledcomposite materials. The cross section of the springs 2, 3, 4, 5 ispreferably rectangular or almost rectangular, a bend or deformationbeing effected preferably only in one plane. At the end areas, caps 24,34 or protective elements can be provided for the springs. The basespring 4 can contain a core made of composite material. The base spring4 with an upwardly directed arch, i.e. oriented towards the adapter 6,is moved or forced into a straight shape by application of a tensileforce or of a bending moment. A spring action is achieved in this way.Such a base spring 4 provides a smooth rollover movement duringmid-stance, on account of a plantar flexion of the toe area duringloading of the heel, since the front end 21 of the forefoot spring 2 isdrawn down when the heel strike occurs. The base spring 4 increases theenergy return, both of the forefoot spring 2 and also of the heel spring3, and thus provides a satisfying sensation when walking, because of theadditional spring resistance. This is achieved by the excursion of thesprings on account of the uniform load distribution resulting from theconnection of the base spring 4 both to the forefoot spring 2 and alsoto the heel spring 3. As has already been discussed, the base spring 4also increases the stability of the prosthetic foot 1, because theapplied loads are divided up between the four spring components 2, 3, 4,5. Overall, this has the effect that the prosthetic foot 1 has thefeatures of an ankle joint, without having to accept any of thedisadvantages of a traditional ankle joint, such as wear, complexconstruction, costs and maintenance.

The coupling element 5 has a number of advantages, for example the factthat the length of the heel support is extended, which leads overall toincreased flexibility. The coupling element 5 reduces the load in thearea of the attachment to the heel spring 3, which again leads toincreased stability. The coupling element 5 further serves as anoverload spring if unusually high loads occur. In the event of unusuallyhigh loads, the coupling element 5 can come into contact with theforefoot spring 2 in the front area or with the base spring 4, dependingon the nature of the load that is applied. In this way, the direction inwhich the load is introduced is changed, which leads to an increasedload-hearing capacity of the entire prosthetic foot 1.

The slit base spring 4 and the slit forefoot spring 2, with theorientation of the slit 26, 46 in the anterior-posterior direction,permit increased medial-lateral mobility of the prosthetic foot 1, whichin turn leads to improved adaptability of the tread surface on theground. The improved adaptability to the ground surface increases thecomfort and stability experienced by the person using the prostheticfoot 1.

With the prosthetic foot 1, various configurations of the springs withdifferent degrees of stiffness can be used, so as to be able to adapt todifferent weight categories for a defined size of the prosthetic foot 1.The modular, reversible mode of construction allows the prosthetic foot1 to be dismantled for maintenance purposes, such that defectiveindividual parts can be replaced and such that the prosthetic foot 1 canbe adapted to a change of weight, to a change of loads, to a change inthe degree of mobility or to the individual requirements of the users.It can be adapted easily by using a spring with a different degree ofstiffness. The modular, reversible design permits a simplified assemblyprocedure, since the individual components are screwed together orfitted into one another. Adhesive bonding of the individual componentsof the prosthetic foot is no longer necessary, although this can becarried out in the area of the receiving means 42, 43 in order to reducewear.

Adapting the degree of stiffness of the prosthetic foot 1 is mainlyachieved by changing the thickness of the individual springs 2, 3,4. Thethicker a spring is, the stiffer it is, unless changes are made. It hastherefore proven advantageous that the receiving means 42, 43 in thebase spring 4 have identical dimensions, which are preferably adapted tothe maximum stiffness, and that adaptation to the respective springdimension is effected using compensating elements that are fitted ontothe springs, cast onto the springs or fitted into the receiving means orinjected in before assembly.

FIG. 7 illustrates further refinements of the invention. As illustratedin FIG. 7, a friction element 71 is inserted between the forefoot spring2 and the coupling element 5. The purpose of this friction element 71 isto eliminate or reduce noise. In addition, the forefoot spring has anelongated slit 26′ which provides more flexibility in rollover. In theembodiment shown in FIG. 7, the bolts 9 attach to adapter 6 by means ofthreaded through holes 72. These holes are covered by a cover plate 73,made of any suitable material such as composite or metal. The coverplate 73 may be attached as a friction fit into grooves in the adapter 6or by adhesive. Caps 74 are shown at the front end of the forefootspring 2. In the embodiment shown in FIG. 7, the forefoot spring 2 ismore or less flat and the caps 74 have corresponding receiving means.Because of the longitudinal slits in the forefoot spring 2 and the basespring 4, it is possible that the springs rotate relative to each otherin a way that the inserted forefoot spring 2 is turned inside thereceiving pockets 42 of the base spring 4. To minimize the torsionalstress along the longitudinal axis of the forefoot spring 2, it isadvantageous to allow a relative rotation movement between the caps 74and the corresponding receiving pockets 42. To achieve this, a conicalor cylindrical design is provided, so that the outer surface of the capscan rotate inside the receiving pockets. A stop can be implemented toset a limit for the turning movement.

FIGS. 7a and 7b are side views of the embodiment shown in FIG. 7 in anunassembled state and an assembled state, respectively.

FIG. 8 illustrates a modification of the base spring 4, similar to theembodiment in FIG. 4a but in which the receiving pockets 42 are providedwith cylindrical or frusto-conical insertion openings 421′ into whichends of the base spring 4 are inserted.

FIG. 9 shows a variation of the embodiment of FIG. 7 in which the caps74′ are cylindrical or frusto-conical.

While the invention has been described in terms of preferredembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims.

1-73. (canceled)
 74. A prosthetic foot comprising: a forefoot spring, aheel spring, and a base spring, the base spring being connected to theheel spring and to the forefoot spring, wherein the heel spring isconnected to the forefoot spring via a coupling element and the couplingelement extends forwards along the forefoot spring at least via oneportion, wherein the coupling element is a spring.
 75. The prostheticfoot according to claim 74, wherein the coupling element, at least inthe unloaded state, extends forwards along part of the forefoot springand parallel to the forefoot spring.
 76. The prosthetic foot accordingto claim 75, wherein the coupling element has an upwardly directedportion and a forwardly directed portion.
 77. The prosthetic footaccording to claim 76, wherein the upwardly directed portion of thecoupling element is oriented substantially vertically.
 78. Theprosthetic foot according to claim 74, wherein the heel spring issecured on a front area of the coupling element.
 79. The prosthetic footaccording to claim 74, further comprising friction material between theforefoot spring and the coupling element, the friction material servingto reduce noise.
 80. The prosthetic foot according to claim 74, whereinthe heel spring is curved and, from its rear end, extends forwards andupwards and has a curvature such that the front end area is orientedhorizontally or at a downward incline.
 81. The prosthetic foot accordingto claim 74, wherein the forefoot spring has a substantially straightforefoot portion which, towards the front, is oriented at a downwardincline.
 82. The prosthetic foot according to claim 74, wherein the basespring has first and second receiving means for the forefoot spring andthe heel spring respectively, into which the forefoot spring and theheel spring are inserted.
 83. The prosthetic foot according to claim 82,wherein the first and second receiving means hold the forefoot springand the heel spring with a form fit.
 84. The prosthetic foot accordingto claim 82, wherein the first and second receiving means are designedas pockets.
 85. The prosthetic foot according to claim 82, wherein thepockets are of a closed design and have insertion openings.
 86. Theprosthetic foot according to claim 85, wherein the insertion openings ofthe first and second receiving means lie opposite each other.
 87. Theprosthetic foot according to claim 82, wherein a pretensioning means isarranged in one of the first and second receiving means and pretensionsthe heel spring and/or the forefoot spring against the base spring orthe receiving means.
 88. The prosthetic foot according to claim 87,wherein the pretensioning means is designed as a spring or elastomerelement.
 89. The prosthetic foot according to claim 87, wherein thepretensioning means is cast in, pushed in, bonded in or secured on theheel spring and/or the forefoot spring.
 90. The prosthetic footaccording to claim 74, wherein the base spring is designed as a tensionmember.
 91. The prosthetic foot according to claim 74, wherein the basespring is designed as a spring arching upwards in the unloaded state ofthe prosthetic foot.
 92. The prosthetic foot according to claim 74,wherein the base spring is pretensioned with a tensile stress in theunloaded state of the prosthetic foot
 93. The prosthetic foot accordingto claim 74, wherein the base spring is designed as an injection-moldedpart.
 94. The prosthetic foot according to claim 74, wherein the basespring is designed in several parts.
 95. The prosthetic foot accordingto claim 74, wherein the base spring is produced from a compositematerial.
 96. The prosthetic foot according to claim 74, wherein thebase spring has a curved middle portion, which is adjoined at both endsby first and second receiving means.
 97. The prosthetic foot accordingto claim 96, wherein the first and second receiving means are integrallyformed on either side of a middle portion of the base spring or securedthereto.
 98. The prosthetic foot according to claim 97, wherein themiddle portion of the base spring is made of a fiber-reinforcedcomposite material.
 99. The prosthetic foot according to claim 74,wherein a connecting means, provided for securing the prosthetic foot toa below-knee shaft, is arranged on the proximal end of the prostheticfoot.
 100. The prosthetic foot according to claim 99, wherein theconnecting means has a shock absorber.
 101. The prosthetic footaccording to claim 99, wherein the forefoot spring is designed as astraight flat spring, the connecting means arranged at a rear portion ofthe forefoot spring and the coupling element designed as a straight flatspring, arranged parallel to the forefoot spring.
 102. The prostheticfoot according to claim 74, wherein the forefoot spring and the basespring have a slit.
 103. The prosthetic foot according to claim 74,wherein the prosthetic foot has a progressive ankle moment profile. 104.The prosthetic foot according to claim 74, wherein, at heel strike,force is transferred at least partially to the forefoot spring via thebase spring.
 105. The prosthetic foot according to claim 104, whereinthe heel spring comes closer to the base spring under heel loading andan anterior portion of the heel spring assembly can contact the basespring under severe loading.
 106. The prosthetic foot according to claim74, wherein the forefoot spring and the base spring are designed, interms of shape and flexural elasticity, in such a way that duringrollover, when the force is initially introduced into the ball region atthe start of loading of the forefoot, the forefoot spring and the basespring come closer to each other by means of each of them bending underincreasing load.
 107. The prosthetic foot according to claim 74, whereinduring forefoot loading, at least part of the load is transferred to theheel spring via the base spring
 108. The prosthetic foot according toclaim 74, wherein the base spring, the heel spring and the couplingelement are designed, in terms of shape and flexural elasticity, in sucha way that during heel strike, under severe loading conditions, the heelspring assembly contacts the base spring at or near the anterior end ofthe heel spring assembly and this contact provides a heel stiffeningeffect.
 109. A prosthetic foot comprising: a forefoot spring, a heelspring, and a base spring, the base spring being connected to the heelspring and to the forefoot spring, wherein the heel spring is connectedto the forefoot spring via a coupling element and the coupling elementextends forwards along the forefoot spring at least via one portion,wherein the coupling element is designed as a spring and the couplingelement has a substantially straight forefoot portion which, towards thefront, is oriented at a downward incline.
 110. A prosthetic footcomprising: a forefoot spring, a heel spring, and a base spring, thebase spring being connected to the heel spring and to the forefootspring, wherein the heel spring is connected to the forefoot spring viaa coupling element and the coupling element extends forwards along theforefoot spring at least via one portion, wherein the coupling elementis designed as a spring and the coupling element has an upwardlydirected portion and a forwardly directed portion.